1. Field of the Invention
The present invention relates to films of the electrophotographic type comprising a transparent film used as recording media in electrophotographic recording apparatus. More specifically, the present invention relates to films of the electrophotographic type for use as recording media for image formation in electrophotographic recording apparatus for overhead projection and the like, and further relates to image forming methods for use with said films in electrophotographic apparatus.
2. Description of the Related Art
Conventionally, electrophotographic apparatus are capable of forming images on films of the electrophotographic type comprising a transparent film made of polyester or the like which are used as recording media in electrophotographic apparatus such as copying machines and which can be projected via an overhead projector and the like.
In recent years, electrophotographic apparatus such as copying machines and the like generally detect the passage of recording media by means of photosensors of the transparent or reflective types using a light source such as light-emitting diodes (LED) or the like to detect the passage of said recording media.
However, when an electrophotographic film comprising a transparent type film made of polyester or the like is used as recording media, the passage of the electrophotographic film is impossible to detect because the wave length of the light emitted from the LED or the like ranges from visible light to infrared light, such that said light is only slightly absorbed or reflected by said electrophotographic film.
Conventionally, in order to detect the passage of electrophotographic film in electrophotographic apparatus of the aforesaid type, a non-transparent member for absorbing or reflecting the light from the LED or the like is provided on a portion of said electrophotographic film, such that the passage of said electrophotographic film can be detected thereby.
Proposed methods for providing non-transparent members for absorbing or reflecting light from an LED or the like on a portion of the aforesaid electrophotographic film include methods for printing a coating on electrophotographic film which cuts 60% or more of the light emitted from an LED or the like, methods for adhering a band of paper, cloth or the like on electrophotographic film, and methods for forming a metallic vacuum deposition layer to block the light of an LED or the like.
When image formation is accomplished via an electrophotographic apparatus using the previously mentioned electrophotographic film with adhered band of paper, cloth or the like, and the toner image formed on said electrophotographic film is fixed on said film via a fixing device of the heat-pressure type, a portion of the aforesaid paper, cloth or the like adhered to the film peels away from the film due to differences in the shrinkage factors of the electrophotographic film and said paper or cloth. This situation is disadvantageous in that it produces problems in discharging the electrophotographic film.
On the other hand, in forming images on electrophotographic film used in electrophotographic apparatus such as copying machines and the like, the electrophotographic film is fed into the electrophotographic apparatus and toner images are typically formed on said film via an electrophotographic process. Thereafter, the film is guided to a fixing device which utilizes a fixing roller comprising a heating roller or the like, such that the toner image formed on said film is fused thereon via the fixing device, thereby producing the toner image on the electrophotographic film.
When film is fed into the electrophotographic apparatus for image formation in the manner described above, the film is softened via the heat applied by the fixing device on said film when the toner image formed on the film is fused thereon by the fixing device. This situation is disadvantageous inasmuch as the electrophotographic film 10 may become rolled up on the surface of the fixing roller 30, as shown in FIG. 7, or the electrophotographic film 10 may not properly feed between the fixing rollers 30, as shown in FIG. 8, such that, in either case, the electrophotographic film 10 becomes jammed within the apparatus.
Various research has been conducted heretofore in regards to means for preventing the electrophotographic film from becoming rolled up on the fixing roller, and improper feeding of the electrophotographic film between the fixing rollers as previously described. For example, one method proposes the electrophotographic film may be constructed so as to have greater thickness, or, other method proposes the electrophotographic film may be formed of heat-resistant synthetic resins.
When the electrophotographic film is constructed so as to have greater thickness, however, certain other disadvantages arise inasmuch as the transparency of said film is reduced, such that when images are formed on said film and projected via overhead projector and the like, the projected image is difficult to see. Furthermore, thermal efficiency is reduced when the toner image is fixed on the electrophotographic film, such that inadequate fusion of the toner image on the electrophotographic film results.
Additionally, still further disadvantages arise when a heat-resistant synthetic resin film is used as the electrophotographic film inasmuch as the transparency of the electrophotographic film is adversely affected due to the typically poor transparency of the heat-resistant resin itself. Furthermore, when images are formed on said film and projected via overhead projector and the like, the projected image is difficult to see in much the same manner as described for film of greater thickness.
In recent years, unique electrophotographic film has been developed wherein said film comprises polyethylene-2,6-naphthalate film having a saturation-contraction ratio of less than 0.3% on both the horizontal and vertical at 180.degree. C., and Young's modulus of 600 Kg/mm.sup.2 or greater on both the horizontal and vertical.
The aforesaid film having the previously described physical properties is unique, and, therefore, expensive. Furthermore, the aforesaid unique film cannot sufficiently eliminate the previously mentioned disadvantages when used as an electrophotographic film for image formation, i.e., the problems of the electrophotographic film becoming rolled up on the fixing roller, and improper feeding of the electrophotographic film between the fixing rollers.